KELLY MCEVERS, HOST:

We've also been talking to people who saw the attack in Barcelona, and you will hear them throughout today's show. We first reached Nafees Hamid by phone. It was a few hours after the attack. And he had just started introducing himself to me when he heard something.

NAFEES HAMID: Well, I'm actually a terrorism researcher based in Barcelona. And so I work here, and I study jihadists linked to radicalization, terrorist organizations and so forth.

UNIDENTIFIED PEOPLE: (Screaming).

HAMID: What? There's another attack, another attack happening. (Unintelligible).

MCEVERS: What?

HAMID: There's madness going on. People are running in every direction.

MCEVERS: OK. Get to safety, please.

HAMID: OK. Thank you. I don't know if that was just a mass panic or what just happened. Hundreds of people came running my way right now.

(CROSSTALK)

HAMID: So I'm not...

MCEVERS: Focus on getting yourself to safety.

We later learned that the police may have been in a shootout with a suspect right around the time we were talking to Hamid, and that might have been what the panic was about. Things did calm down, and I asked Nafees Hamid to tell me what he had seen when the initial attack happened. He was in the main square when it happened.

HAMID: I had been at Placa Catalunya just actually saying goodbye to a friend. He was off, so he was off to London, was visiting me. So I just said goodbye to him there as he caught the bus to the airport. And I was just roaming around the area a little bit actually, just taking in some of the summer buzz in Barcelona. It's obviously a top tourist destination in Europe. Placa Catalunya and Las Ramblas are probably two of the most touristic, busiest areas of Barcelona at the height of the tourist season in mid-August. So I was just kind of in the area, just taking a stroll and seeing - just taking in some of the mood, the energy, really.

MCEVERS: And then what did you - what was the first thing you heard or saw?

HAMID: I didn't hear the attack itself. What I heard was - I just saw people running, kind of like what just happened to me right now...

MCEVERS: Yeah.

HAMID: ...Just hundreds of people running in one direction. And then I just heard police sirens coming from every single direction. They were very quick to respond. Luckily there already is a very large police presence in Placa Catalunya because it is such a big touristic destination. I think within just a couple of minutes, I heard a helicopter in the sky. So it was a very quick response.

MCEVERS: Wow. And then what did you do?

HAMID: Well, I backed off, like, with everyone else, tried to get to a safer area. I tried to find out what was happening. I started getting a flood of text messages and WhatsApp messages, people telling me what's going on, seeing if I'm OK. I went back to my apartment for a second just to see what was going on in the news. And then I started walking back over to the area up until the police line, obviously respecting the police rules to not go any further than they wanted us to go and just observe it from there. And I've been out on the street since then.

MCEVERS: What does your instinct say to you about what happened given what you know in your research?

HAMID: You know, there was a white van. There was a white van in the London attacks. We know since 2014 ISIS has been calling for people to get behind a car and to carry out attacks, to run people over with their cars, which has been - even been mimicked by far-right members, like what we saw in the Finsbury Park mosque attack in London or what we just saw in Charlottesville. So there's definitely this reciprocity between extreme right-wing movements and then jihadist movements in terms of their respective acts of domestic terrorism.

But I mean the most important thing as a researcher is to caution people to not jump to conclusions. I think that's probably the most important thing at this moment. That can stoke a lot of fires. There's a lot - already a lot of tension in Europe and the United States, and we need to show reticence and be careful and not to jump to any conclusions.

MCEVERS: As we just heard, there was what appeared to be maybe a panic that was not linked to another attack that just happened around you.

(SOUNDBITE OF SIRENS)

MCEVERS: How's everybody doing? And now I - and now we hear sirens. How's everybody doing? I mean did people seem - people must obviously be pretty on edge.

HAMID: Yeah. People are scared. I'm seeing police go in one direction. I'm seeing ambulances go in another direction. I just saw ambulances going in the direction of supposedly where that panic was coming from. Again, I don't know what actually motivated it. People have rushed into buildings. Stores have allowed people into their stores and closed their metal gates, covering their store windows - seeing people crying, people shaking, people trying to get home. And of course there's a lot of onlookers and people standing around and watching and seeing what's happening. So, yes, on edge would be correct.

MCEVERS: Nafees Hamid, thank you so much for talking to us.

HAMID: No problem, my pleasure.

MCEVERS: That's Nafees Hamid, a terrorism researcher with Artis International. ISIS has since claimed responsibility for the attack. Transcript provided by NPR, Copyright NPR.